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Are there any doors or windows above the deck where the vent will be. If not.

With the clearence to the deck and being at an inside corner. Going through the deck is probably your best bet.
The install manual will have the number of ells you can use for the length of vent pipe.
Being that close to the wall, I doubt you'll be close to the limit.

Contractors have 2 more questions about venting..

1. Can they reduce the pipe size from 3inch to 2 inch BEFORE they go through the outside wall, or after the pipe is outside (and then elbow it up and throught the deck - there are 3 elbows required after the pipe is outside)

2. Can the INTAKE remain in the house, if there is enough ventilation in the furnace room?

Refer to the install instructions for when they can reduce.
Since its going to go through the deck yet, I think you need to maintain the 3" untill outside.
Most 90&#37; units, lose some efficiency if they use indoor air.
Refer to the install manual for proper combustion air intake locations.

You need 50 CF of free air space per 1000 BTUs input. So if your furnace is a 100,000 BTU input, you need 5000 CF of space in your basement. Or vents allowing flow from other rooms into the are where the furnace is located.

Thanks, they'll follow that advice & verify with manuals

The unit is 75,000 BTU and the furnace room was designed with two unobstructed vents for that purpose. The basement itself is about 1000sq feet and 90% of it is open space (no walls), so it should get decent intake ventilation.

He thanks you for your advice and will now use 3 inch until he gets outside the wall.

The contractor has the installation manual that tells him what he can and can't do with reguards with installing your new furnace. He also has to conform to all applicable code requirements. Let them worry about the number of elbows etc.. I doubt there would be any issue with elbow count from what you've explained and showed.

His question, I'm thinking, was whether you would mind the venting coming up through your deck and terminating there. That's a personal preference that he left up to you. Count yourself lucky that you were home to be asked and didn't return to find something done that you were going to be upset with.

Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

1. Can they reduce the pipe size from 3inch to 2 inch BEFORE they go through the outside wall, or after the pipe is outside (and then elbow it up and throught the deck - there are 3 elbows required after the pipe is outside)

2. Can the INTAKE remain in the house, if there is enough ventilation in the furnace room?

Again, it's a Rheem Prestige 90.

THANKS !!!!

Sounds like you're doing a good amount of work yourself helping this contractor. Did you check to make sure he's got you covered by workmans comp insurance, that you're accumulating vacation and sick days, having the correct amount of taxes withheld from your paycheck and doesn't forget to let you take the required amount of breaks.

Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

That's the only spot for the pipe.

To House: The furnace is closest to that wall and going out that wall (over the A/C unit, about 2 inches under the deck), is the shortest way to 'open air' (8-10feet from wall). He using 3 inch PVC for the whole length, and he said he's going to insulate (though I don't know how) the pipe.